Fabry disease is an X-linked lysosomal storage disease of glycolipid catabolism caused by a deficiency of ?- galactosidase A (?-Gal A). Severe extremity pain is usually the initial manifestation of Fabry disease and often begins in childhood. Patients exhibit progressive accumulation of glycolipids in many tissues, with the most prominent being renal cells, cardiomyocytes, and vascular endothelial cells. This intracellular accumulation leads to progressive tissue and organ damage (i.e., end-stage renal disease, cardiomyopathy, stroke), resulting in a severely compromised quality of life and premature death. Currently, the only FDA-approved treatment is enzyme replacement therapy (ERT) in which recombinant ?-Gal A is given by intravenous infusion every two weeks. This regimen is extremely expensive and potentially immunogenic, and efforts to increase ERT potency would be highly advantageous to both Fabry patients and the healthcare system. The cellular target for Fabry ERT is the cation-independent mannose 6-phosphate receptor (CI-MPR). In addition to binding lysosomal enzymes modified with mannose 6-phosphate, CI-MPR binds insulin-like growth factor 2 (IGF2). Therefore, IGF2 conjugation to ?-Gal A has the potential to increase enzyme efficacy. Similar to the ~70 other lysosomal storage diseases, the pathophysiology of Fabry disease is poorly understood. Although the only available animal model, the Fabry mouse, recapitulates microscopic glycolipid accumulation in its tissues, it lives a normal lifespan and does not exhibit the clinical phenotype such as progressive chronic kidney disease that is observed in humans. The Medical College of Wisconsin has recently generated a rat model of Fabry disease on a background susceptible to stimulus-induced kidney disease. We confirmed the absence of ?-Gal A activity and demonstrated by mass spectrometry the accumulation of plasma glycolipids in this ?-Gal A- deficient rat. The goals of this application are to 1) create?-Gal A-IGF2 fusion proteins to increase ERT potency, and 2) characterize the newly generated Fabry rat as a model of Fabry nephropathy and pain. Specific Aim 1: ?-Gal A-IGF2 fusion proteins will be rationally designed, expressed in mammalian cells, and biochemically characterized through a variety of techniques (i.e., enzyme assays, surface plasmon resonance). Cellular uptake experiments followed by administration of the new constructs to the Fabry rat will be accomplished, and plasma glycolipid reduction will be monitored. Successful constructs have the potential to improve glycolipid reduction in patients. Specific Aim 2: The Fabry rat will be extensively characterized and histological specimens will be analyzed for glycolipid accumulation by both microscopy and mass spectrometry. Behavioral assays will be used to determine the suitability of the Fabry rat as a pain model. A metabolic specialist will be consulted throughout this process to correlate findings in the rat with the human disease. The rat model will serve as a critical resource to study the pathogenesis of Fabry disease and evaluate new therapeutic strategies.